This invention relates to treadmills with trampoline-like surfaces and, more particularly, to an improved suspension system for suspending the mat or belt between a supporting surface in such an apparatus.
Treadmills utilize an endless moving belt that allows an individual to walk, jog or run in place. Treadmills are useful not only for exercise, but for rehabilitation programs and medical testing such as the "stress test" which is commonly used. There is a demand for treadmills in indoor health clubs since many clubs are not able to build a running track and a treadmill provides the capability of a well-rounded exercise program.
Most treadmills are formed with a thin, endless belt which travels over a supporting surface so that the belt can withstand the weight of the individual using it. The rigid surface beneath the belt in these treadmills can cause shin splints or other stress-related injuries to the legs of the user. The use of treadmills of this design in rehabilitation programs is limited because of the impact on the legs of the users.
It has been found that a treadmill which utilizes a trampoline-like surface with a built-in resiliency reduces impact on the legs of the users to the point where such a machine can be used as a primary therapeutic aid for rehabilitation from leg injuries. because it significantly reduces the wear and tear on the legs of the user.
U.S. Pat. No. 4,938,473 which issued on Jul. 3, 1990 describes a treadmill with a trampoline-like surface. The suspension system of this treadmill is made from a pair of springs spaced at an angle between each carrier and the belt to provide lateral support and stability for the belt. However, belts which utilize springs have a tendency to be unstable and the spring fatigue causes the belt to become slack. Further, springs have been found to increase the expense of maintenance to the machine due to spring failure and spring cuts.
An improvement over a spring suspension system is described in U.S. application Ser. No. 657,439 which was filed on Feb. 19, 1991, which is incorporated as though fully set forth. In this application an improved treadmill with a trampoline-like surface having rail carriers attached directly to the lateral edges of the belt is disclosed. The suspension system includes rail carriers extending over the lateral edges of the belt with a bolt that extends downward from the rail carrier, being inserted through grommets in the belt and secured on the belt underside by a nut. The rail carriers provide tension to the belt.
In order to maintain the correct amount of tension with this suspension system, the dimensions of the width of the belt and the placement of the grommets along the belt edge are extremely important. Very little variation in these dimensions is adjustable in the manufacture of the treadmill. Additionally, the belt has a tendency to stretch over time creating decreased belt tension. This causes excessive noise and instability of the carriers as they roll around the rails of the treadmill.
Due to the problems mentioned above, an improved suspension system that eliminated the use of springs or a rigid belt-carrier connection would improve the structure and performance of the apparatus.